JPH07322624A - Power converter - Google Patents

Abstract

PURPOSE:To continue operation without causing overcurrent even if a DC measurement circuit for obtaining the feedback signal of constant current control fails in a power conversion device for performing constant current control so that the DC output current of the power conversion device matches a command value. CONSTITUTION:The title power converter for performing constant current control so that the DC output current of the power converter matches a command value is provided with a DC measurement circuit 30 for directly detecting a DC output current from a DC current transformer 3 and an AC equivalent measurement circuit 70 for calculating the DC output current from an AC measurement current 7A obtained by an AC current transformer 7. Further, the title converter is provided with a comparator 8 for comparing a detection signal 7B of the AC equivalent measurement circuit 70 with a detection value 3A of the DC measurement circuit 30, a selection circuit 9 for responding to an output signal 8A of the comparator 8, and a switching device 10 for automatically switching a current 10A for controlling constant current from the detection value 3A of the DC measurement circuit to the detection signal 7B of the AC equivalent measurement circuit according to a switching signal 11 of the selection circuit 9.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a power converter for controlling a DC output current with a constant current, and more particularly to a power converter capable of continuing operation even if a DC current transformer detecting the DC output current has a problem. Regarding

[0002]

2. Description of the Related Art In a conventional device, a DC current transformer measures an output current of a power converter, and constant current control is performed so that the measured value matches a set value. Hereinafter, in FIG. 3, the conventional DC output current that controls the DC output current with a constant current The DC output current 2 of the power converter 1 is detected by the DC current transformer 3. The detection signal 3A of the DC current transformer 3 is given to the constant current control circuit 4. The constant current control circuit 4 adjusts the gate timing given to the thyristor of the power converter 1 so that the preset DC output current and the DC current transformer detection signal 3A match.

[0003]

In the above-mentioned conventional power conversion device, since the output current detection means of the power conversion device 1 is only the DC current transformer 3, a problem occurs in the DC current transformer 3, Current transformer 3 rather than DC current 2 flowing in the main circuit
When the detected current 3A of 3A becomes small, the power conversion device 1 performs constant current feedback control to detect the detected DC current 3A.
The switching timing of the elements constituting the power converter 1 is adjusted so that the (secondary current of the DC current transformer) and the command value match, and the DC output current 2 is operated to increase.
That is, if the current transformer secondary current 3A becomes smaller than the actual main circuit current due to a malfunction of the DC current transformer 3, an excessive current may flow through the load 12 and damage the load 12 and devices.

According to the present invention, the power converter side detects that a malfunction has occurred in the DC current transformer 3, and prevents an excessive DC current from flowing by mistake in the main circuit. An object of the present invention is to provide a power conversion device that can be continuously operated without stopping the power conversion device even if the above problem occurs.

[0005]

In order to achieve the above-mentioned object, the present invention has a configuration as shown in FIG. 1, in which a detected value of a direct current measuring circuit for directly detecting a direct current output current from a direct current transformer is used. An AC equivalent measurement circuit that calculates a DC output current detection value by calculating from an AC measurement current obtained by an AC current transformer, and a comparator that compares the detection signal of the AC equivalent measurement circuit with the detection value of the DC measurement circuit. , A selection circuit responding to the output signal of the comparator, and a switching device for automatically switching the constant current control current from the DC current transformer detection current to the AC equivalent measurement circuit detection signal by the selection circuit switching signal It is a thing.

[0006]

According to the power converter having the above-mentioned configuration, even if the DC current transformer malfunctions and the DC current transformer detection current becomes smaller than the actual main circuit current, the DC current detection function is provided. By switching to the AC equivalent measuring circuit for backup, it is possible to prevent the constant current control circuit from erroneously increasing the DC output current and preventing an excessive current from flowing to the load or the power conversion device. Further, when the DC current transformer fails, the operation of the power converter can be maintained by switching the DC current detection function to the backup AC equivalent measuring circuit.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a flow chart for explaining the operation.

In FIG. 1, 1 is a power converter, 2 is a direct current output current, 3 is a direct current transformer forming a direct current measuring circuit 30, and 3A is a detection current of the direct current measuring circuit 30 (hereinafter simply referred to as a direct current detection current). 4) constant current control circuit, 5 AC power supply, 6 transformer for transformer, 7 AC current transformer, 7A is secondary current of AC current transformer 7, 70 is secondary current of AC current transformer 7. An AC equivalent measurement circuit for calculating a DC current corresponding to the DC detection current 3A from the current 7A, 7B is a detection current of the AC equivalent measurement circuit 70 (hereinafter, simply referred to as a DC equivalent detection current), and 8 is a DC detection current 3A. And a direct current equivalent detection current 7B are compared with each other, and a comparator 9 generates an output signal 8A when the difference exceeds a preset value, and 9 is switched by applying the output signal 8A of the comparator 8. Selector circuit for generating signal 11, 1 By the switching signal 11 is applied, a Setsu換Ru switching device to direct the equivalent detection current 7B constant current control current 10A from the DC detected current 3A.

As described above, in the conventional apparatus, when the DC measuring circuit 30 has a problem, the function of the constant current control circuit 4 causes the DC detected current 3A to match the command value.
The DC output current 2 was increased by adjusting the switching timing of the elements that constitute the power conversion device 1. This may cause the power conversion device 1 to operate by following an erroneous detection current and damage the load 12 and devices due to overcurrent.

On the other hand, as the circuit for detecting the DC output current 2 of the power conversion device 1, the following two detection circuits have been conventionally known. One is a DC measurement circuit 3 that uses a DC current transformer 3.
The direct current measuring circuit 30 which directly measures the output current 2 at 0, and the other, without using the direct current transformer 3, uses the alternating current transformer 7 instead of the alternating current 7A of the transformer 6 for the power converter. AC equivalent measurement circuit 70 for detecting and calculating DC current
There is.

Since the DC measuring circuit 30 directly measures the DC current 2, it has the advantage of high detection accuracy, but the DC current transformer 3
However, compared to the AC current transformer 7, the circuit is complicated and the frequency of failure is high.

The AC equivalent measuring circuit 70 has the advantage of less failure, but is not suitable for the power converter 1 which has a large detection error of the DC current 2 and requires high detection accuracy. In general, the DC current detection value 3A obtained by the DC measurement circuit 30,
It is considered that the DC equivalent detection currents 7B obtained by the AC equivalent measurement circuit 70 are almost the same, and when a large difference occurs between these two detection values and the detection value of the DC measurement circuit 30 is low. There is a high possibility that the DC current transformer 3 will malfunction.

According to the present invention, both the DC measuring circuit 30 and the AC equivalent measuring circuit 70 are provided in the power converter 1, and the highly accurate detection value normally obtained by the DC measuring circuit 30 is used for control as described above. In addition, a large difference occurs between the detection values 3A and 7B of the two measurement circuits 30 and 70, and the DC detection current 3A of the DC measurement circuit 30 is lower than the DC equivalent detection current 7B of the AC equivalent measurement circuit 70. In this case, the DC current transformer 3 is considered to be defective and the DC measurement circuit 30 is disconnected from the constant current control circuit 4, and instead the DC equivalent detection current 7B of the AC equivalent measurement circuit 70 is used for control. . Hereinafter, a specific description will be given with reference to FIG.

In the present invention, the AC equivalent measurement circuit 70 calculates the DC detection current 3A detected by the DC measurement circuit 30 using the DC current transformer 3 and the AC current 7A detected by the AC current transformer 7. The difference between the DC equivalent detection currents 7B is obtained by the comparator 8 and this difference signal 8A is given to the selection circuit 9. In the selection circuit 9, the difference signal 8A obtained by the comparator 8 and
Detection value 3 of DC measuring circuit 30 and AC equivalent measuring circuit 70
Use A and 7B. The evaluation described in FIG. 2 is performed. (1) Difference signal 8A between the DC detection current 3A of the DC measurement circuit 30 and the DC equivalent detection current 7B of the AC equivalent measurement circuit 70
(Output of the comparator 8) becomes equal to or greater than a preset set value,
Moreover, when the DC detection current 3A of the DC measurement circuit 30 is smaller than the DC equivalent detection current 7B. (If the DC detection current 3A is detected to be smaller than the actual DC current 2 due to a malfunction of the DC measurement circuit 30, an excessive current flows in the main circuit of the device due to the function of the constant current control, and the load 12 and the device are damaged. (2) When the detected value 7B of the AC equivalent measuring circuit 70 is stable, but the DC detection current 3A of the DC measuring circuit 30 fluctuates significantly. (Unstable) When the condition (1) or (2) is satisfied, the selection circuit 9 considers that a failure has occurred in the DC measurement circuit 30, and sends a switching command 11 to the switching device 10. The switching device 10 has a switching signal 1
When 1 is received, the current command value 10A for the constant current control circuit 4
Is switched from the DC detection current 3A of the DC measurement circuit 30 used until then to the DC equivalent detection current 7B of the AC equivalent measurement circuit 70.

Under the condition (1), the DC equivalent detection current 7B of the AC equivalent measuring circuit 70 is the DC measuring circuit 3
If it is smaller than the DC detection current 3A of 0, it is an abnormality of the measurement circuit, but the DC current 2 of the main circuit is smaller than the target value and does not cause damage to the load 12 or equipment. DC detection current of measuring circuit 30 3A
Use only to issue an alarm that indicates an abnormality in the measurement circuit. Further, it is necessary to select the switching device 10 so that the signal 10A to the constant current control circuit 4 does not change suddenly at the time of signal switching.

[0016]

As described above, according to the present invention, in a power converter that performs constant current control, when a failure occurs in a DC measurement circuit that uses a DC current transformer, a DC current for constant current control is used. By automatically switching the detection signal (feedback signal) from the DC detection current of the DC measurement circuit to the DC equivalent detection current of the AC equivalent measurement circuit, an abnormal increase in the DC output current of the power converter is prevented, and The operation can be continued without stopping the converter.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is a flow chart for explaining the operation of the selection circuit shown in FIG.

FIG. 3 is a block diagram showing a configuration example of a conventional power conversion device.

[Explanation of symbols]

1 ... Power conversion device 2 ... DC output current 3 ... DC current transformer 3A ... DC current transformer detection current 4 ... Constant current control circuit 5 ... AC power supply 6 ... Conversion bulletin transformer 7 ... AC current transformer 7A ... AC current transformer Current secondary current 7B ... AC equivalent measuring circuit detection current 8 ... Comparator 8A ... Comparator output signal 9 ... Selection circuit 10 ... Switching device 11 ... Switching signal 12 ... Load 30 ... DC measuring circuit 70 ... AC equivalent measuring circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yusuke Ashizaki 1-1-1, Shibaura, Minato-ku, Tokyo Inside Toshiba Head Office

Claims (1)

[Claims] 1. A DC measuring circuit for directly detecting a DC output current from a DC current transformer, and an AC current transformer in a power converter for performing constant current control so that a DC output current of the converter matches a command value. AC equivalent measurement circuit that calculates the DC output current by calculating from the AC measurement current obtained by, a comparator that compares the detection signal of the AC equivalent measurement circuit and the detection value of the DC measurement circuit, and the comparator By the selection circuit that responds to the output signal and the switching signal of the selection circuit,
A power converter equipped with a switching device that automatically switches the constant current control current from the detection value of the DC measurement circuit to the detection signal of the AC equivalent measurement circuit.